A femtocell will hereinafter be described in brief.
Femto is a prefix in the metric system, denoting a factor of 10−15 or 0.000000000000001. Hence a femtocell or FBS refers to an ultra-small indoor Access Point (AP) for low-power home use or office use. Although the term “femtocell” is sometimes interchangeably used with “picocell”, the former is used in the sense of a more advanced cell. The femtocell is a small cellular base station (BS) connected to a broadband router and functions to connect 2nd Generation (2G) and 3rd Generation (3G) voice and data to a backbone network of a mobile communication service provider via the Digital Subscriber Line (DSL).
The above-mentioned femtocell has the following advantages.
Recently, a new research paper has proposed a method for the femtocell to expedite the spread of 3G technology and greatly increase indoor coverage. Up to 2011, it is expected that the number of femtocell users throughout the world will increase to about one hundred and two million, and the number of access points (APs) serving as BSs will also increase to about thirty-two million.
Femtocells can expand cell coverage and increase the quality of voice service. Mobile communication service providers are expecting that subscribers may be familiar with 3G by providing data service via femtocells. The femtocells are also called femto base stations (FBSs) or femto Base Transceiver Stations (femto BTSs).
In summary, a communication system using femtocells offers the following benefits 1) to 4): 1) Cell coverage improvement, 2) Infrastructure cost decrease, 3) New service offering, 4) Fixed Mobile Convergence (FMC) acceleration.
One or more femtocells may be grouped on a service basis or geological area basis. For example, a femtocell group that can access only a specific MS may be referred to as a Closed Subscriber Group (CSG). A femtocell BS (FBS) recognizes a CSG ID of the MS so that it allows access of only the MS subscribed to the CSG.
FIG. 1 shows an example of a femtocell arrangement structure for use in an overlay network.
Referring to FIG. 1, a backbone network of the femtocell BS is directly connected to an Internet Service Provider (ISP) network connected by wire, and a Femtocell GateWay (FGW) may be located at an access point between the backbone network and the ISP network. The FGW may be used as an access point for communication with a Macrocell (or Macro) Base Station (MBS).
The FGW may be directly connected to femtocell BSs, or may be located between a core network and an ISP network so as to be an integrated server for each ISP. In addition, the system may guarantee its communication with a macrocell (or macro) BS (MBS) through a Core Network Service GateWay (CNS GW) or an Access Service Network GateWay (ASN GW) irrespective of the location of the FGW. In the overlay network, the MBS may transmit/receive or store some or all information units for FBSs.
If femtocell BS configuration is completed, the MBS may recognize other information including FBS location information. Therefore, the MBS may directly communicate with the FBS through an air interface.
In this case, the macro BS including a Home Femto BS of an MS and a Closed Subscriber Group (CSG) femto BS may be referred to as an Overlay Macro BS.
FIG. 2 shows an example of a femtocell arrangement structure in a non-overlay network.
If many users are temporarily crowded at a boundary among MBSs in a non-overlay structure, FBSs may be installed at a boundary among macrocells. In this case, the MBS may not store all information of FBSs therein. At this time, the FGW may serve as an access point where the FGW can communicate with the MBS in the same manner as in the overlay structure.